I am constantly bewildered by the power a religion can have on someone - this is a prime example. Rejecting there own kids because someone told them it is the right thing to do!!!!
I never "quite" reached the stage you have - managed to keep contact - but it has never been the same.
You could try and back down a bit - remove videos etc. On the other hand they may not actually follow-through with shunning you.
No easy answers.
Good luck.....The Scotsman